We Somtimes plow and then disk - other times - we just disk. It depends on what we are planting and why. On some plots we want to build up the organic matter in the soil. We do this by turning it over every year - then disking it level. Especially plots that were corn the year before - or that will be corn again.
Sometimes - if we are planting a small seed like clover, rye, or brassica - we mow -Spray roundup - Wait 2-3 weeks - then disk it out. Then we roll it with a cultipacker - Seed/fertilize - then roll it with a cultipacker again
Lastly - if we had planted Roundup-soybeans the year before - and we want to plant clover - we might just frost seed - or not disk at all - just broadcast - fertilize - and roll with the cultipacker.
So - there is no easy answer - different plots and situations require different techniques. A disk is probably most important - because a plow is no good without it - and - works OK (not great though) - with spraying roundup.
FH